(1) Field of the Invention
The present invention relates generally to aqueous silane compositions and, more particularly, to aqueous silane compositions for use in making absorbent surfaces, such as masonry, water repellent.
(2) Description of the Prior Art
Aqueous silane compositions have become important for making absorbent surfaces, such as masonry, water repellent. The following discussion is generally taken from U.S. Pat. Nos. 4,877,654 and 4,990,377 to Wilson. The entire disclosures of Wilson '654 and '377 are hereby incorporated by reference.
The utility of silanes, especially alkoxysilanes, as masonry water repellents is widely known. Compositions currently in use employ solutions of silanes in various organic solvents such as alcohol, e.g., U.S. Pat. Nos. 3,772,065, to Seiler and U.S. Pat. No. 4,342,796, to Brown et al. or hydrocarbons, e.g., U.S. Pat. No. 4,525,213 to Linn. Principal limitations of such solvent type compositions include the toxicity and the flammability of the solvents employed.
Aqueous silane compositions which are non-toxic and non-flammable have become important as effective masonry water repellent compositions. See, U.S. Pat. Nos. 4,433,013, to Puhringer, 4,517,375 to Schmidt and 4,648,904 to DePasquale and U.S. Pat. Nos. 4,877,654 and 4,990,377 to Wilson. Such compositions can have an important drawback, however, in that the pH may tend to drift and then the silane reacts with water and hydrolyses. See, e.g., U.S. Pat. Nos. 2,683,674 to Hatcher et al. and U.S. Pat. No. 4,175,159, to Raleigh. This reduces efficacy by reducing the content of active, water-repellent ingredient. Moreover, the pH of the system may shift when additives are included such as a biocide, which is commonly added to retard growth of fungi and the like.
Although the stability of the water-containing emulsions has been enhanced to some extent by refrigerating them, or the problem of reduced efficacy can be avoided by using the emulsions soon after preparation, both expedients are not cost-effective and may in some cases cause waterproofing contractors to go back to the above-mentioned solvent borne, non-aqueous compositions.
In some cases, the pH of the system has been adjusted to increase the rate of resin formation, see e.g., U.S. Pat. Nos. 4,552,910 to Deubzer et al. and U.S. Pat. No. 4,228,054, to Ona et al. Wilson, in U.S. Pat. No. 4,877,654 teaches that by selecting appropriate silanes (largely water insoluble) and appropriate emulsifiers, water-based, normally hydrolyzable silane emulsions may be prepared that are hydrolytically stable if the pH is maintained in a predetermined pH stable range, typically 6-8, with a buffering compound such as sodium bicarbonate. However, Wilson only teaches concentrations of less than about 60 percent and, in fact, his preferred compositions are about 40 percent. Significant savings in packaging and shipping could be obtained if the concentration could be increased since most of the current products are water which could easily be re-added at the site where the composition is being applied.
Thus, there remains a need for a new and improved aqueous silane compositions for use in making absorbent surfaces, such as masonry, water repellent which is hydrolytically stable for a long period without necessarily requiring a separate buffering compound while, at the same time, may be prepared in much higher concentrations to reduce packaging and shipping costs.